Since the development of the first commercially successful internal combustion engine in the 1860's by Otto and Langen, there have been constant attempts to improve the internal combustion engine. The results of those attempts are apparent everywhere and the internal combustion engine is common throughout the world and used in countless applications, including but not limited to transportation, power generation, construction, agriculture, recreational vehicles, and garden implements, to name a few. In addition to multiple applications, internal combustion engines are available for a variety of fuels, including diesel, gasoline and natural gas.
Although there are several other types of internal combustion engines such as the gas turbine and rotary, the most common type is the reciprocating piston engine. This engine operates in a cycle with four phases: intake, compression, power (expansion), and exhaust. The piston travels between a Top Dead Center position (hereafter abbreviated as “TDC”), which denotes its highest point of travel, and a Bottom Dead Center position (hereafter abbreviated as “BDC”), which denotes it lowest point of travel. The distance the piston travels between TDC and BDC is a fixed distance, and is commonly referred to as the stroke of the piston. This type of engine is either a two-stroke cycle or a four-stroke cycle. A two-stroke cycle engine requires two piston strokes (or one full revolution of the crankshaft) to complete all phases of operation, while the four-stroke cycle engine requires four piston strokes (or two full revolutions of the crankshaft) to complete all phases of its operation. Separation of each phase of operation is not a distinct division from the other phases. Time, in the form of crankshaft angle of rotation, is ‘borrowed’ from each of the phases such that each phase is transitioned into the next by overlapping or, in the case of the two-stroke cycle engines, combining phases.
In the typical reciprocating piston engine, the piston travels in a cylinder bore or cylindrical housing between TDC and BDC, and a connecting rod joins the piston to a crankpin on the crankshaft. The crankpin is located a set distance from the centerline of the crankshaft. In this typical configuration, the path of the crankpin as the crankshaft rotates is a circle, and the diameter of the circle is identical to the stroke value. The various parameters within this configuration such as piston diameter and stroke (determined by the crankpin location) can be changed but the basic linkage remains the same. Attempts to enhance an internal combustion engine within this configuration have been limited to some extent by the physical and mechanical properties of the materials used to construct the engine, as well as the thermodynamic properties of the fuel and its delivery into the cylinder.
There have been attempts to modify the basic linkage described above by altering the crankshaft action, varying the stroke, or changing the Compression Ratio (hereafter abbreviated as “CR”). For example, Moore U.S. Pat. No. 6,453,869 sought to increase efficiency by extending the piston dwell point at TDC and improving connecting rod leverage through a crankshaft provided with an eccentric member. Shaw U.S. Pat. No. 6,526,935 sought to increase fuel efficiency and torque by having the orbiting crankshafts trace a heart shaped pattern and providing means to adjust the CR during operation. In Gonzales U.S. Pat. No. 5,927,236, it is claimed that thermo-efficiency of an internal combustion engine was increased by varying the stroke length and imposing a larger expansion stroke and a shorter intake stroke. Schaal U.S. Pat. No. 5,158,047 claims to increase net engine efficiency by decreasing piston velocity in the first half of the power stroke by allowing more time for cylinder pressure to increase.
The unrealized advantages associated with the previous attempts have been overcome by the present invention. In contrast to previous attempts to alter the crankshaft action by extending piston dwell at TDC, the present invention maximizes piston dwell at BDC. Although there have been many attempts to cause a piston to dwell at or near TDC, or to maximize the leverage that acts to turn the crankshaft, it would appear that such a dwell should allow the fuel mixture trapped within the combustion chamber to more fully burn and reach a higher initial pressure while the available volume is small. An increased leverage or moment arm, caused by the geometry of the engine components and combined with this increased pressure, should result in more force acting to rotate the crankshaft and result in increased torque output from the engine. However, there are several reasons why these advantages cannot be realized.
A piston that dwells at or near TDC causes the fuel mixture (or air in a diesel) to preheat before the ignition phase is initiated by the introduction of a spark or fuel. All surfaces within the engine are heated by the combustion of the fuel mixture from previous power strokes, and the newly inducted fuel mixture absorbs some of this heat, in addition to the heat produced during the compression cycle. Heating the fuel mixture prior to having it trapped within the cylinder reduces its density, which means less fuel mixture is ultimately trapped for compression and power production. Detonation of the fuel mixture during this dwell period is very likely and would force the lowering of the CR to a point where engine efficiency would suffer. In order for a piston to be held at or near its TDC position while the crankshaft continues to rotate and build leverage, particularly after the combustion process has been initiated, considerable force must be applied to the piston. The rising cylinder pressure, combined with the available leverage, would tend to force the piston down the cylinder bore, which would apply a force to the crankshaft that would attempt to rotate the crankshaft in the opposite direction than intended. Until the piston is traveling down in the cylinder bore, all effort to hold it at or near TDC is against the intended direction of rotation. The net result of this negative effort is a reduction in the engine's output.
Dwell of the piston at or near TDC requires a considerable amount of crankshaft rotation to be committed to this effort and, since time is elapsing, less time and crankshaft rotation will be available to complete the other phases of engine operation. Time consumed at or near TDC results in less time being available to push the piston down the bore, scavenge the exhaust gases from the cylinder, and/or to refill the cylinder with the next fuel mixture. Without sufficient time to separate and accomplish these individual events completely, the engine's efficiency will suffer due to the overlapping of the required events, and some mixing of exhaust residue with the fresh fuel mixture will result.
Holding the piston at or near TDC while the crankshaft continues to rotate results in an increase in the lever arm on the crankshaft. Intuitively, an increased lever arm would seem to allow more torque or rotational force to be transmitted to the crankshaft with the same amount of force applied. However, such is not the case in the referenced attempts.
Viewed idealistically, the output of an internal combustion engine during a single power phase is dependant on only two variables that affect a piston of specific area: 1) The force derived from the pressure the burning fuel mixture produces within the cylinder, and 2) the distance that that pressure pushes the piston down the cylinder bore before being vented. Once the pressure within the cylinder is released, the power phase ends, even though the piston continues to travel down the cylinder bore to BDC. If the variables of force and distance remain unchanged, the total torque output of the power phase will always be the same, regardless of the crankshaft design or configuration employed. When advantages are claimed from increasing the dwell of the piston at or near TDC, there is no mention of the loss of time that the engine will suffer in getting the next fuel mixture into the cylinder. In a similar manner, claims of increases in leverage or moment arm fail to mention that on a per-degree basis, the pressure above the piston's crown falls at a more rapid rate, destroying any potential torque gains. The increased leverage causes the piston to move a greater distance for every degree of crankshaft rotation, which increases the trapped volume within the cylinder. This lowers the pressure within the cylinder and results in a loss of force to act on the increased moment arm. The total amount of torque applied to the crankshaft over the duration of the entire power phase will be no greater than the amount of torque produced by a conventional style of crankshaft. Therefore, any increases in engine output must be gained through increasing the work done on the piston, yet prior attempts that altered crankshaft motion were unable to achieve this result.
Work done on the piston is calculated by using the formula for work, which is as follows:Work=Force×Distance
The inventive crankshaft is able to increase the work done on the piston through gains in cylinder force (pressure×piston area) and travel (distance.)
Using this formula in the context of a piston driven engine, the work done on a single piston is the product of the force provided by the pressure produced from the heat of fuel combustion acting on the crown of the piston and the distance the piston travels in its bore while that pressure acts on it. While the formula and the concept are fairly straightforward to understand, the accurate depiction of the work produced involves some detailed analysis. For instance, the pressure produced within a combustion chamber and cylinder bore varies directly with the volume of that cylinder space. If the piston is at the beginning point of its travel away from TDC at the beginning of the power phase, the pressure is high due to the minimum combustion space above it. As the pressure acts on the piston's crown and causes it to move down the bore, the volume within the combustion space and cylinder increases due to the displacement of the piston. This in turn lowers the pressure within the combustion space considerably. At some point in the travel of the piston, the exhaust phase is initiated, either by the piston uncovering an exhaust port or by an exhaust valve opening. Through either mechanism, an escape path for the trapped pressure is provided. As soon as the exhaust port or valve is opened, the force driving the piston down the cylinder bore is diverted out of the cylinder and the work done on the piston comes to an end. It must be remembered that the piston continues to move to the end of its full travel (to BDC) with no force acting to push it further down its bore. Work on the piston is no longer being performed.
Since the pressure within the cylinder is changing with the piston movement, the force acting on the piston's crown is also changing. Therefore, a single value for force cannot be directly entered into the work formula. However, the force within the cylinder can be calculated at various points along the piston's travel, based on the cylinder volume at those points and the initial starting pressure. The total distance traveled by the piston while acted upon by cylinder pressure is then summed at each point (this can also be found through integration.) In other words, the volume above the piston crown can be accurately calculated by the use of simple geometry and knowing the piston's position in the cylinder, and the resulting pressure found through the application of Boyle's law. This simplified view does not address thermodynamic considerations, but the example is relevant in this application.
There are several advantages to extending piston dwell at BDC. The piston will reach TDC quicker than an engine with a similar stroke and operating at a similar rate of speed, allowing less time for the trapped fuel mixture to absorb heat from the surrounding surfaces and preheat. This will tend to ward off the undesirable condition of detonation, and it will then be possible to raise the CR to attain more efficiency.
Ignition timing is usually set to occur at some point as the piston is still approaching TDC during the compression stroke. Typically, a spark is introduced in the cylinder at a point in the crankshaft rotation before TDC (hereafter abbreviated as “BTDC”), which, through geometry, can be equated to a distance that the piston is away from its TDC position. This is done to enable the spark to ignite the fuel mixture while the cylinder pressure is rising due to compression. Time is required to achieve a complete burn to occur, but the rate of burn is also influenced by the rate of pressure rise within the cylinder. If the piston is dwelling at BDC, it will be moving a greater distance per degree of crankshaft rotation during the rise to the top of the cylinder bore. If the spark is to occur at the same distance from TDC as in a standard engine, through geometry it can be seen that the number of crankshaft degrees before the piston reaches TDC will be less. The rate of pressure rise will be greater than in a standard engine, so the ignition phase can be made to occur at fewer degrees of crankshaft rotation before TDC. This will lessen the negative work done on the piston, which will tend to rotate the engine in the opposite direction than intended, and the net result will be a greater power output.
By allowing the piston to recede away from TDC quickly, there is considerably less time for the heat from the combustion of the fuel mixture to soak into the surrounding surfaces. The heat retained within the combustion gases is more fully utilized to produce pressure to act upon the piston's crown. Since less heat is deposited within the surrounding cylinder surfaces, the next inducted fuel mixture charge will have a cooler environment to enter into, resulting in a denser fuel charge, promoting efficient combustion and greater engine output.
By maximizing the piston dwell at or near BDC, the piston will travel to the bottom region of the bore in less time than a conventional engine or one that has its piston dwell at or near TDC could accomplish. This will occur when all engine designs are rotating at the same rate, generating the same number of Revolutions Per Minute (hereafter abbreviated as “RPM”.) In the engine that has its piston dwell at or near BDC, there will be an increased amount of time that the piston will be at the bottom of the piston stroke. Therefore, the piston can be moved a greater distance down the cylinder bore with pressure above it and still have the proper amount of time to scavenge the cylinder and refill it with fresh fuel mixture. Also, the distance the piston moves during the compression phase can be increased as well. This means that a larger volume of fuel mixture can be trapped at the beginning of every compression phase. If the actual CR were to be retained at a value identical to a standard engine, the volume of the combustion chamber must be increased as well, resulting in even greater trapped volume than would normally occur. Since the output of the engine is closely tied to the volume of fuel mixture inducted into the cylinder during each intake phase, the additional trapped volume will produce more heat and pressure within the cylinder during the power phase and will result in an increase in engine output.
Since the volume of the intake charge is now enhanced, the rate of pressure drop during the entire power phase will be slower. From TDC to the end of the power phase, the starting and ending cylinder pressures will be identical to those in a conventional engine with identical displacement, but the piston will have traveled a greater distance in the process. The actual cylinder pressure for every increment of piston movement will favor the cylinder with the larger initial volume of fuel mixture since the changes in piston position will have less influence on the total volume containing the pressure.
In the present invention, during the time that the piston will dwell at or near BDC, cylinder pressure will be at its lowest value, having allowed for the maximum expansion of the combustion gases to occur against the piston crown. During the exhaust phase, sufficient time is now available to allow the exhaust gases to leave the cylinder under their own pressure differential and without having to be pumped out by the piston. This will result in less work for the piston to do on the exhaust gases remaining in the cylinder at the end of the exhaust phase. The net result to the engine's power output will be increased since little or no energy from the power stroke will have to be invested in pumping pressurized exhaust gases out of the cylinder.